1. Field
Percutaneous delivered medical device.
2. Background
Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating heart disease. In a typical procedure, a catheter assembly having a balloon portion is introduced percutaneously into the cardiovascular system of a patient via the brachial or femoral artery. The catheter assembly is advanced through the coronary vasculature until the balloon portion is positioned across an occlusive lesion. Once in position across the lesion, the balloon is inflated to a predetermined size to radially compress the atherosclerotic plaque of the lesion against the inner wall of the artery to dilate the lumen. The balloon is then deflated to a smaller profile to allow the catheter to be withdrawn from the patient's vasculature.
Restenosis of the artery commonly develops over several months after the procedure, which may require another angioplasty procedure or a surgical by-pass operation. Restenosis is thought to involve the body's natural healing process. Angioplasty or other vascular procedures injure the vessel walls, removing the vascular endothelium, disturbing the tunica intima, and causing the death of medial smooth muscle cells. Excessive neoinitimal tissue formation, characterized by smooth muscle cell migration and proliferation to the intima, follows the injury. Proliferation and migration of smooth muscle cells (SMC) from the media layer to the intima cause an excessive production of extra cellular matrices (ECM), which is believed to be one of the leading contributors to the development of restenosis. The extensive thickening of the tissues narrows the lumen of the blood vessel, constricting or blocking blood flow through the vessel.
To reduce the chance of the development of restenosis, therapeutic substances may be administered to the treatment site. For example, anticoagulant and antiplatelet agents are commonly used to inhibit the development of restenosis. In order to provide an efficacious concentration to the target site, systemic administration of such medication however often produces adverse or toxic side effects for the patient. Local delivery is a preferred method of treatment in that smaller total levels of medication are administered in comparison to systemic dosages, but are concentrated at a specific site. Local delivery, thus, produces fewer side effects and achieves more effective results.
One commonly applied technique for the local delivery of a therapeutic substance is through the use of a medicated, implantable prosthesis, one example of which includes a stent. A stent coated with a polymeric carrier, which is impregnated with a therapeutic substance, can be deployed at a selected site of treatment. The polymeric carrier allows for a sustained delivery of the therapeutic substance. A disadvantage associated with the use of medicated stents is that the quantity of the substance that can be impregnated in the polymeric carrier is limited. In order to increase the capacity of the polymeric carrier, the amount of polymeric material employed, the profile (e.g., thickness) of the coating must be increased to accommodate the quantity of the substance used. An increase in the profile of the coating significantly limits the applications for which the stents can be used.
One technique for the local delivery of a therapeutic substance into the tissue surrounding a bodily passageway is disclosed in U.S. Pat. No. 5,464,395 to Faxon et al. U.S. Pat. No. 5,464,395 discloses a catheter including a needle cannula slidably disposed in a needle lumen and a balloon, which is coupled to the distal end of the catheter. When the balloon is inflated, the needle lumen is brought into close engagement with the tissue and the needle cannula can be moved between a position inboard of the catheter distal surface and a position where the needle cannula is projected outboard of the catheter to deliver the therapeutic substance to the tissue.
It has been observed, that in most instances, the inflation and deflation of the balloon causes the needle lumen to form a tortuous pathway, which the needle cannula must traverse to reach the tissue. Unfortunately, under these conditions, the needle cannula can become stuck in the pathway, such that it cannot be advanced. For example, the sharp tip of the needle cannula can gouge, become lodged in, or puncture the catheter wall. Curving the tip of the needle may help to prevent some damage, but it can require that the needle lumen be made undesirably larger to accommodate the curved needle tip and may result in inconsistent needle engagement with the tissue.